The present disclosure relates to a battery system, which comprises a plurality of battery cells and a temperature control element, which has a thermally conductive connection to the battery cells via a temperature control surface. In its interior the temperature control element has a temperature control channel, which is routed via an inlet on the supply-flow side and via an outlet from the temperature control element on the return-flow side.
The disclosure further relates to a motor vehicle comprising the battery system.
It is becoming apparent that in future new battery systems, on which very high demands are placed with regard to reliability, safety, performance and service life, will be increasingly used both in stationary applications, such as wind power stations, in hybrid and electric motor vehicles, and in electronic appliances, such as laptops and mobile phones.
In order to ensure the safety and functioning of lithium-ion batteries, it is necessary to operate the lithium-ion cells within a predefined temperature range. During operation the lithium-ion cells generate heat, firstly in the form of the Joule effect, which can be described by the electric current and the internal resistance of a lithium-ion cell, and also by virtue of the heat produced due to reversible phenomena in the lithium-ion cell. This heat must be dissipated, in order to prevent heating of the lithium-ion cell beyond a critical operating temperature—and hence overheating of the lithium-ion cell.
In order to operate a lithium-ion battery in favorable temperature ranges, the lithium-ion cells are connected to a temperature control system. According to the type of temperature control fluid used, this system can in principle be divided into:    1. air cooling,    2. coolant cooling and    3. refrigerant cooling.
The choice of temperature control fluid is determined according to the level of temperature control performance required.
As a rule multiple cells are combined to form a module and multiple modules are in turn combined to form a battery. In the case of temperature control using a temperature control plate one or more battery modules are simultaneously temperature-controlled by a temperature control plate through thermal conduction. Aluminum is commonly used as material for a temperature control plate, or another material having at least equivalent heat-conducting characteristics is used.
The temperature control plate heats up the lithium-ion cells, for example when starting on cold days, or cools them, for example during high-load operation at high ambient temperatures. In many technical applications the lithium-ion cells are temperature-controlled via their underside. Due to the overall space available it is often necessary to distribute the battery cells over multiple temperature control plates within a battery. For optimum battery operation these temperature control plates have to be hydraulically adjusted according to their thermal loads. Here distributor blocks serve to distribute the mean temperature control mass flow and to deliver it to the individual temperature control plates via flexible hose lines. The return flow is correspondingly fed in the reverse direction from each temperature control plate to a central collector by means of flexible hoses and led out of the battery housing. For designing such a temperature control system load cycles are generally used, by means of which it is possible to predict the temperature rise within the lithium-ion battery under known thermal boundary conditions.
When cooling multiple battery cells using one temperature control plate with temperature control fluid flowing through it, the temperature of the temperature control fluid steadily increases due to the absorbed heat losses from the battery cells as the flow passes through the temperature control plate. As a result, those battery cells which the temperature control fluid reaches only later are cooled with a warmer temperature control fluid than those batteries which have already been cooled by the temperature control fluid previously. Given an approximately equal power loss from the battery cells, this inevitably results in a higher temperature for the battery cells cooled by the already heated temperature control fluid, than for those that have been cooled by the still cooler temperature control fluid. For optimum battery performance and service life it is however necessary to regulate the temperature of all its battery cells to an approximately equal (optimum) temperature.
The publication DE 10 2006 061 270 A1 discloses a battery, a battery module and a method for operating a battery module. Here the evening-out of the temperature to an extent favorable to the operation of the battery cells is brought about by introducing, between the battery cells, a thermally conductive battery bed consisting of a metal body or a highly thermally conductive plastic mass, which may also additionally contain metal particles. A desired temperature balance between the battery cells can thereby be produced; the temperature can also be maintained at a required level for longer and if necessary can also be emitted more rapidly. Balancing and charging electronics exert additional influence on the maintenance of an optimum temperature during the discharging and charging cycles of the battery cells.